Aifei Pan

Rutile TiO2 Flocculent Ripples with High Antireflectivity and Superhydrophobicity on the Surface of Titanium under 10 ns Laser Irradiation without Focusing

We report on the formation of rutile TiO2 flocculent laser-induced periodic surface structures (LIPSSs) with high antireflectivity and superhydrophobicity on the surface of titanium under 10 ns 1064 nm laser irradiation without focusing. The center part of the Gaussian laser beam is used to deposit flocculent structure and the edge part used to produce LIPSSs. The melt and modification thresholds of titanium were determined first, and then, the melt and modification spot-overlap numbers, several responsible for the formation of flocculent structure and LIPSSs, were introduced. It is found that both the melt and modification spot-overlap numbers increase with an increase in laser fluence and spot-overlap number, contributing to the production of flocculent LIPSSs. LIPSSs are obtained with the modification spot-overlap number above 300, and the amount of flocculent structures increases with an increase in the peak laser fluence and spot-overlap number. Then, considering that the fine adjustment of the melt and modification spot-overlop numbers in one-time line scanning is quite difficult, the composite structure, of which both LIPSSs and flocculent structures are distinct, was optimized using laser line scanning twice. On this basis, a characterization test shows the sample full of the flocculent LIPSSs represents best antireflectivity with the value around 10% in the waveband between 260 and 2600 nm (advance 5 times in infrared wavelengths compared to the initial titanium surface), and shows the no-stick hydrophobicity with the contact angle of 160° and roll-off angle of 25° because of the pure rutile phase of TiO2.

Three-dimensional micro-nano-hierarchical porous structures based on the deposition of the ablated material by picosecond pulses

This study was performed using picosecond pulses to obtain the three-dimensional micro-nano-hierarchical porous structures on the surface of titanium via the combination of the ablation and the deposition of ablated particles. For the repetition rate of 100 kHz and the scanning speed of 10 mm/s, there were secondary nano-tree-like micro-nano structures via the deposition of the ablated material formed on the primary microstructures. However, when the scan speed decreased, the primary microstructures were invisible owing to too much material deposition. When the repetition rate increased to 500 kHz, the ablated particles were irradiated by the posterior pulse before deposition onto the surface of material, and agglomerated into spidernet-like nanostructures. Then, the upper layer of the secondary micro-nano structure was molten and came into micro-nano porous fractal structures. Both the secondary micro-nano porous structures showed the hierarchy in the vertical and horizontal direction of the surface of titanium. Contact angle measurement after 3 months indicated that the nano-tree-like micro-nano structures showed super-hydrophilcity, and the spidernet-like nano and micro-nano porous fractal structures showed super-hydrophobicity.

Fabrication of microstructures by rear-side picosecond laser irradiation of two-layer PMMA

Micro-structures offer superior functions such as superhydrophobicity, selfcleaning, anti-wear and drag reduction. In this paper, various microstructures were fabricated by rear-side picosecond laser irradiation of two-layer materials. The material of underlying layer was commonly commercial available ink; the material of surface layer was PMMA. The high light absorptivity of underlying material result in significantly reduced absorption depth. The laser source could therefore be regarded as plane heat source, leading to better surface morphologies after the mater-laser interaction. The results showed that convex structures were obtained at a lower laser fluence; with increase of laser fluence, a doughnut-like structures were obtained; with further rise of laser fluence, bowl-like structures would be obtained. Moreover, the size of microstructures could be tuned by adjusting laser processing parameters such as laser power, frequency and laser-mater interaction time. This method provides an insight for fabrication of functional surface.